Work in LMB has led the way towards the ambitious goal where stem cells can be used to replace tissue damaged by neuro-degenerative diseases that cause the loss of neurons or glial cells. Our most successful studies show that large numbers of functional dopamine neurons can be derived from mouse embryonic stem cells. These are the types of neurons that are lost in Parkinson?s patients, a disease that afflicts more than one million Americans. Our team, for the first time, has now successfully cultivated highly enriched populations of nerve cells from human embryonic stem cells in vitro. These nerve cells were synaptically active and able to produce dopamine. In vitro strategies to generate large numbers of functional somatic cell types are required to apply human ES cells in medicine. Our recent work shows that aggregation of human ES cells rapidly generates differentiated cells expressing combinations of genes and morphologies characteristically found in the major embryonic and extra-embryonic founding cell types of the body. The developmental potency of these precursors was confirmed by subsequent steps that generated hepatocytes as well as dopaminergic neurons. These data show that human ES cells efficiently generate the major cell types of the gastrula and that these cells can mature in a few steps to give highly enriched populations of differentiated somatic cells. The development of a general technology that provides access to dopamine neurons and to many other cell types of the human body has major implications in medicine.